Pit vipers, along with several of their snake cousins, marry
two senses to better locate prey at night: sight and a
heat-detecting ability. Deep pits, which lie on each side of
the snake's face between the nostril and the eye, are capable
of sensing the warmth given off by a human hand held a foot
away. Each pit has its own "field of vision" which overlaps
slightly with the other, so that the pair work
stereoscopically in the same way that eyes do. Heat and
visual data are sent, via the optic nerve, to the pit-viper's
brain, where the two types of data are transposed into a
single image.